Refrigerating apparatus with hot gas defrost



J. W. JACOBS REFRIGERATING APPARATUS WITH HOT GAS DEF'ROST Filed Sept. 16, 1957 I I 1/ 1 11 1/ 1 1 XXX/1 11 1 l/ /1 May 17, 1960 INVENTOR. James M. Jacobs 1g His Attorney United States Patent REFRIGERATING APPARATUS WITH HOT GAS DEFROST James W. Jacobs, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application September 16, 1957, Serial No. 684,158 2 Claims. (Cl. 62-156) In refrigerating systems such as are shown in Patent 2,672,020, issued March 16, 1954, in which the second evaporator operates upon a defrosting cycle, it is usually desired to increase the speed of defrosting and to reduce length of the defrosting periods. It is also desired to prevent the flow of liquid refrigerant into the cvaporators during the defrosting periods.

.It is an object of this invention to provide a simple means to introduce hot gas into the second evaporator during the idle period of the compressor and to aid defrosting.

It is another object of this invention to provide a simple means for improved defrosting and also to prevent the flow of liquid refrigerant into the evaporators and to unload the compressor during the defrosting period.

'These and other objects are attained in the form shown in the drawings in which a normally open solenoid valve connects the top of the condenser with the continuously open suction conduit to deliver hot gas to the second evaporator and also equalize pressures and prevent the flow of liquid refrigerant during the idle period of the motor-compressor. The motor-compressor unit is energized by a thermostatic switch operating upon a defrosting cycle responsive to the temperature of the second evaporator. The solenoid valve is energized to close simultaneously with the operation of the motor-compressor.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

Figure l is a vertical sectional view through a household refrigerator embodying one form of my invention;

Figure 2 is a view, partly diagrammatic, of the refrigerating system shown in Figure l; and Figure 3 is a schematic wiring diagram for the system shown in Figures 1 and 2.

Referring now more particularly to Fig. 1, there is shown an insulated refrigerator cabinet 20 provided with an upper above-freezing compartment 22 and a lower below-freezing compartment 24 separated by the insulated wall 26. The insulated compartment 24 is surrounded on four sides by a freezing evaporator 28. This freezing evaporator 28 is supplied with liquid refrigerant from the sealed motor-compressor unit 30 which delivers compressed refrigerant to the condenser 32 from which the liquefied refrigerant flows through a receiver 33 and a continuously open capillary tube refrigerant expansion device '34. The freezing evaporator 28 has the refrigerant conduits therein arranged so as to trap liquid refrigerant therein. Suificient refrigerant evaporates in the evaporator 28 to keep the compartment 24 at low freezing temperatures such as 0 to -5 F.

2,936,594 Patented May 17,1960

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The surplus of liquid and evaporated refrigerant passes upwardly from the outlet of the evaporator 28 through a conduit 36 extending upwardly to a liquid trap 38 from which the liquid refrigerant flows into the plate evaporator 40. The trap '38 keeps the evaporator 28 filled with liquid refrigerant. This plate evaporator 40 is located in a vertical passage 42 provided in the rear wall of the cabinet 20 behind the compartment 22. A fan 44 at the bottom of the passage 42 withdraws air from the compartment 22 and forces it past both sides of the plate evaporator 40 so that it is cooled thereby. This air is returned to the compartment 22 through the grille 46. The remainder of the liquid refrigerant evaporates in the evaporator -40 and returns to the suction inlet of the compressor through the continuously open suction conduit 48 connecting with the inlet of the motor-compressor 30. The operation of the motor-compressor unit 30 is controlled by the thermostatic switch 50 having a thermostat bulb 52 clamped to the plate 40. The switch is set to operate on a defrosting cycle. For example, the switch 50 may be set to close at 36 F. and to open at 0 F. This switch may be of the type shown in my Patent 2,762,888, issued September 11, 1956.

In order that the freezing compartment 24 is kept at a low average temperature according to my invention, the bypass conduit '54 is provided, connecting the discharge conduit of the motor-compressor unit 30 with the suction conduit 48. This bypass conduit 54 is provided with a normally open solenoid valve '56 which is electrically connected in parallel with the motor-compressor unit 30 and in series with the switch 50, as shown in Fig. 3. By this arrangement, whenever the switch 50 opens at its lower temperature limit such as 0 F. the motor-compressor unit and the valve '56 will be simultaneously deenergized. This insures that whenever the motor-compressor unit 30 is idle, the valve 56 will open. The opening of the valve '56 will allow hot gas from the top of the condenser to flow through the bypass conduit 54 and the suction conduit 48 into the plate evaporator 40 which is located at the highest level of the refrigerating system. The sudden reduction in pressure also causes the liquid in the warm condenser to vaporize and continue this flow of hot gas. The hot gas will condense within the cold plate evaporator 40 and heat given off in the condensing process will rapidly heat up this plate evaporator and melt whatever frost which has accumulate-d thereon during the running cycle of the system. This hot gas, therefore, will quickly heat up the plate evaporator 40 so as to assure its rapid rise to the temperature at which the switch '50 will close to restart the system. This will reduce the length of the cycle and increase the operating periods so that the freezing compartment will be kept at a very low average temperature even though the evaporator 40 is being defrosted during each idle period.

The opening of the valve '56 during the idle period also equalizes the pressures in the high and low sides of the system during the idle period, unloading the compressor. Without such 'an equalization the high pressure in the condenser would force warm liquid refrigerant into the evaporator 28 during the idle period. The pressure within the low side of the system during the idle period is higher than the suction pressure during the operating period so that any evaporation would take place at temperatures above the refrigerating temperatures it is desired to maintain in the compartment 24.

By equalizing the pressures between the high and low sides of the refrigerating system, there is no longer any pressure differential remaining to move the liquid refrigerant from the condenser 32 in the evaporator 28, consequently, this liquid refrigerant will not flow into the evaporator 28 until the next running cycle. The next running cycle will quickly lower the pressure within th low side side of the system to the point at which the liquid refrigerant will evaporate at temperatures low enough to produce the refigerating effect desired in the the, sompa m nt ,4- In this ay, th q d era is mor a n a eously e a d he c p m n 24 is kept at a lower average temperature.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be nnderstood that other forms might be adopted, as, may come within the scope of the claims which follow.

What is claimed is a follows:

1. A refrigerator cabinet including insulated Walls enclosing a freezing compartment and an above freezing compartment, a first evaporator associated with 7 said freezing compartment and having an inlet and an outlet, :1 second evaporator associated with said above freezing compartment having a continuously open connection connecting its inlet to the outlet of said first evaporator and having an outlet, said connection having a portion extending substantially above the bottom of said second evaporator to form a trap, a motor compressor unit having an inlet and an outlet, a condenser having an outlet and an inlet provided with a continuously open hot gas connection connecting with said outlet of said unit, a refrigerant expansion device connecting the outlet of said condenser and the inlet of said first evaporator, a continuously open suction conduit connecting the outlet of said second evaporator and the inlet of said unit, a bypass connection provided with a valve connecting said hot gas connection and said suction conduit for delivering hot gas from the condenser to the second evaporator, and means for closing said valve whenever said unit operates and for opening said valve whenever said unit is idle.

2. A refrigerator cabinet including insulated walls enclosing a freezing compartment and an above freezing compartment, a first evaporator associated with said freezing compartment and having an inlet and an outlet, a second evaporator associated with said above freezing compartment having a continuously open liquid trap connection connecting its inlet to the outlet of said first evaporator and having an outlet, a motor compressor unit having an inlet and an outlet, a condenser having an outlet and aninlet provided with a continuously open hot gas ection connectin with said outl t of said u it, a refrigerant expansion, device connecting the outlet of said condenser and the inlet of said first evaporator, a continuously open suction conduit connecting the outlet of said second evaporator and the inlet of said unit, a bypass connection provided with a valve connecting said hot gas connection. and said suction conduit for delivering hot gas from the condenser to the second evaporator, a thermostatic switch means responsive to the temperature of said second evaporator for starting and stopping said motor compressor unit at predetermined temperatures above and below freezing respectively, and electrical operating means energized coincidentally to the operation of said motor compressor unit for closing said valve to cause said evaporators to be cooled below freezing and deenergized to open said valve to allow hot gas from the condenser to flow into said second evaporator when said unit is stopped to increase the speed of defrosting.

References Cited in the file of this patent UNITED STATES PATENTS 2,430,938 Leeson Nov. 18, 1947 2,492,970 Curry Jan. 3, 1950 2,631,441 Shoemaker Mar. 17, 1953 2,667,757 Shoemaker Feb. 2, 1954 2,678,545 Zearfoss May 18, 1954' 2,805,555 Schumacher Sept. 10, 1957' 

